Background of the Invention
The present invention relates to a hydrostatic transmission (hereinafter referred to as HST) for vehicle that is interposed in a drive-power transmission path between a drive power source and a driving axle, and a power train for vehicle between the drive power source and the driving axle.
It is known that the HST interposed in the drive-power transmission path between the drive power source and the driving axle is provided with a PTO unit for driving a working device. FIG. 9(a) is a model view illustrating a drive-power transmission in the arrangement that a conventional HST with a PTO unit is applied to a vehicle that has a front axle serving as a driving axle and is provided on the front side of the vehicle with a mower or any other working device.
As illustrated in FIG. 9(a), the HST with the PTO unit includes a hydraulic pump unit with a pump shaft operatively connected to the drive power source, a hydraulic motor unit with a motor shaft for outputting the drive power through the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit, a PTO unit with a PTO shaft operatively connected to the pump shaft, and an HST housing accommodating the hydraulic pump unit, the hydraulic motor unit and the PTO unit, in which the PTO shaft has a front end extending forwardly through the HST housing.
In some cases, a demand exists for a wide range of speed change of the driving axle and reduced load applied to the HST serving as a main speed change device. In that case, a mechanical transmission serving as an auxiliary speed change device is additionally interposed between the HST as the main speed change device and the driving axle. FIG. 9(b) is a model view illustrating a drive-power transmission path between the drive power source and the driving axle (front axle) in which the HST with the PTO unit and the mechanical transmission are interposed.
Here, comparing the distance between the front end of the PTO shaft and the front axle (hereinafter referred to distance L) in the arrangement of FIG. 9(a) with the distance L of the arrangement of FIG. 9(b), the former arrangement is: L=L1, and the latter arrangement is: L=L1+L2, in which L2 represents the length of the mechanical transmission with respect to a fore-aft direction of the vehicle.
The front end of the PTO shaft is connected to the mower or any other working device via transmission parts such as a connecting rod with a universal joint. Accordingly, the variation of the distance L necessitates the modification of the transmission parts, the working device and any other associated parts.
Taking for example the vehicle that is provided with the mower as the working device having an elevation function, the variation of the distance L invites not only variation of the length of the connecting rod but also variation of the elevation height of the mower.
That is, since the front end of the PTO shaft serves as a fulcrum for the mower during the upward or downward movement, a simply elongated the elongation of the transmission shaft by L2 simply causes the mower to have a different elevation height. Therefore, in order to equalize the elevational height of the mower between the vehicles of FIGS. 9(a) and 9(b), there arises a necessity to modify a hydraulic piston for elevation of the mower or any other parts.
There thus exist the arrangements with only the main speed change device interposed in the drive-power transmission path, and both the main and auxiliary speed change devices interposed therein. In either arrangement, a demand exists for non-variation of the distance between the front end of the PTO shaft and the driving axle. In other words, a demand exists for the arrangement holding the distance between the front end of the PTO shaft and the driving axle constant regardless of the distance between the driving axle and the main speed change device.
The auxiliary speed change device is an optional member that is provided according to a specification of the vehicle. Therefore, regarding parts constituting the power train between the drive power source and the driving axle excepting the auxiliary speed change device, it is preferable to render those parts commonly usable as many as possible for both arrangements with and without the auxiliary speed change device.
The present invention has been conceived in consideration of the above prior arts. It is an object of the present invention to provide an HST that is capable of effectively limiting the variation in distance between an end of the PTO shaft and the driving axle, even if the distance between the driving axle and the HST is varied.
It is another object of the present invention to provide a power train for vehicle that is capable of being adapted to or matching arrangements with or without the auxiliary speed change device or modifications of the same, or meeting any other demands.
To achieve the above objects, there is provided a hydrostatic transmission for vehicle interposed in a drive-power transmission path between a driving power source and a driving axle for non-stepwisely changing the speed of the vehicle. The hydrostatic transmission includes an HST housing; a hydraulic pump unit disposed within the HST housing and having a pump shaft with first and second ends extending in a fore-aft direction of the vehicle away from each other, in which the first end is positioned closer to the driving axle, and the second end is positioned away from the driving axle and operatively connected to the driving power source; a hydraulic motor unit disposed within the HST housing and having a motor shaft for outputting the drive power from the motor shaft whose speed is non-stepwisely varied in cooperation with the hydraulic pump unit; a PTO unit disposed within the HST housing and having a PTO shaft extending in the fore-aft direction of the vehicle, the PTO shaft being operatively connected to the pump shaft; a charge pump unit for replenishing pressurized hydraulic fluid to a hydraulic circuit, the hydraulic circuit hydraulically connecting the hydraulic pump unit with the hydraulic motor unit, the charge pump unit including a charge pump body that is driven through the first end of the pump shaft, and a charge pump case connected to the HST housing through its wall closer to the driving axle for supporting the charge pump body; the PTO shaft having an one end closer to the driving axle, the one end extending outwardly through the HST housing to have an outer extension positioned outside of the HST housing; and the charge pump case being designed so as to bearing-support the outer extension of the PTO shaft.
According to the HST having the above arrangement, the outer extension of the PTO shaft is bearing-supported by the charge pump case that is connected to the HST housing. Therefore, the variation in distance between the second end of the PTO shaft and the driving axle can be effectively limited, even if the distance between the driving axle and the HST is varied. As a result, the common working device that is driven through the PTO shaft and the common drive power transmission mechanism for transmitting the drive power to the working device can be used for both the arrangements where the HST only is interposed in the drive-power transmission path and where the HST, and the mechanical transmission and/or the PTO device are interposed therein.
In the hydrostatic transmission having the above arrangement, the PTO unit preferably includes a hydraulic clutch device for on/off of the driver power transmission from the pump shaft to the PTO shaft. The charge pump unit also preferably includes a flow divider for dividing the pressurized fluid from the charge pump body to the one for replenishment to the hydraulic circuit and the other for actuation of the hydraulic clutch device, in which the flow divider is disposed within the charge pump case.
The first end of the pump shaft preferably extends outwardly through the charge pump case. The hydrostatic transmission also preferably includes an auxiliary pump unit detachably connected to the pump case for receiving the driving power through the first end of the pump shaft.
According to another aspect of the present invention, there is provided a power train for vehicle between a driving power source and a driving axle. The power train includes a transfer device disposed between a main speed change device that is operatively connected to the driving power source and a differential gear device that transmits the drive power to the driving axle. The transfer device includes a driving shaft and an output shaft. The driving shaft is disposed along a main drive-power transmission axis and operatively connected to a main output shaft of the main speed change device. The main transmission axis is coaxial with the main output shaft, and the output shaft is disposed along the main drive-power transmission axis for outputting the drive power to the differential gear device. With this arrangement, the speed can be stepwisely changed between the driving shaft and the output shaft.
With the power train of the above arrangement, the speed change range available in the drive-power transmission path can easily be widened. Also, by replacing the transfer device with a different one, the specification of the power train can easily be modified. That is, merely mounting or dismounting the transfer device, or modifying the same achieves matching to various specifications of the vehicle.
According to another aspect of the present invention, there is provided a power train for vehicle between a driving power source and a driving axle. The power train includes a transfer device disposed between a main speed change device that is operatively connected to the driving power source and a differential gear device that transmits the drive power to the driving axle. The transfer device includes a driving shaft and an output shaft. The driving shaft is disposed along a main drive-power transmission axis and operatively connected to a main output shaft of the main speed change device, in which the main transmission axis is coaxial with the main output shaft. The output shaft is disposed along the main drive-power transmission axis for outputting the drive power to the differential gear device, in which the drive power is transmitted between the driving shaft and the output shaft. The transfer device also includes an extension extending past the main speed change device in the direction orthogonal to the main drive-power transmission axis, a PTO shaft supported on the extension in such a manner as to be substantially parallel to the main drive-power transmission axis, and a drive-power transmission mechanism for transmitting the drive power synchronized with the output shaft to the PTO shaft.
With the power train having the above arrangement, the PTO shaft that takes off the drive power synchronized with the driving axle can be effectively prevented from interfering with the main speed change device. Thus, the drive-power transmission mechanism disposed on the downstream side of the PTO shaft can be relatively flexibly designed.
In the power train having the above arrangement, the drive-power transmission mechanism preferably includes a driven shaft that is disposed between the main drive-power transmission axis and the PTO shaft in parallel thereto, a first gear train for transmitting the drive power from the driving shaft to the driven shaft at a predetermined speed reducing ratio, a second gear train for transmitting the drive power from the driven shaft to the output shaft at the same speed reducing ratio as the predetermined speed reducing ratio, and a third gear train for transmitting the drive power from the driven shaft to the PTO shaft at the same speed reducing ratio as the predetermined speed reducing ratio.
With the power train having the above arrangement, the PTO shaft can effectively be rotated in synchronization with the output shaft, while sharing in part the common parts between the drive-power transmission line for the PTO system and the drive-power transmission line for the vehicle run. Thus, the transfer device can be manufactured compact as compared with the arrangement that the PTO drive power is taken off through the output shaft of the transfer device.
The power train preferably has the first gear train including an idle gear that is relatively rotatably supported on the driving shaft, and a first driven gear that is relatively non-rotatably supported on the driven shaft to be meshed with the idle gear; the second gear train including a second driven gear that is relatively non-rotatably supported on the driven shaft, and an output gear that is relatively non-rotatably supported on the output shaft to be meshed with the second driven gear; the third gear train including a PTO gear that is meshed with either one of the first and second driven gears to transmit the drive power to the PTO shaft. In this arrangement, the speed reducing ratio of the first driven gear with respect to the idle gear, the speed reducing ratio of the output gear with respect to the second driven gear, and the speed reducing ratio of the PTO gear with respect to the first or second driven gear are the same.
The transfer device preferably includes a clutch member that is relatively non-rotatably and axially slidably supported on the driving shaft. The clutch member is adapted to selectively take a position enabling connection between the driving shaft and the idle gear, a position enabling connection between the driving shaft and the output shaft, and a neutral position between both the positions, enabling shutdown of the drive-power transmission from the driving shaft to the output shaft.
With the arrangement above, through shifting operation of the clutch member, the output shaft and the PTO shaft can be brought into non-outputting state, or the output shaft and the PTO shaft can have speeds changeable in synchronization with each other.
The transfer device preferably includes a counter shaft that is disposed coaxially with the PTO shaft and a slider that is relatively non-rotatably and axially slidably on the PTO shaft and the counter shaft. The PTO gear is supported on the counter shaft via a one-way clutch. The slider is adapted to selectively take a non-outputting position enabling disconnection between the counter shaft and the PTO shaft, a forced outputting position enabling connection between the counter shaft and the PTO shaft while being in meshing engagement with the PTO gear, and a middle position between the non-outputting position and the forced outputting position, enabling connection between the counter shaft and the PTO shaft while being out of the meshing engagement with the PTO gear.
With the arrangement above, it is possible to easily change the outputting state of the PTO shaft. Specifically, through shifting operation of the slider, it is possible to easily change the mode of the PTO shaft between a mode enabling forced synchronization of the PTO shaft with the output shaft, a mode enabling shutdown of the drive power transmission from the output shaft to the PTO shaft when the PTO shaft rotates at a higher speed than the output shaft, and a mode enabling shutdown of the drive power transmission to the PTO shaft.